The present invention relates to heat-transferable security stamps and processes for forming the same. More particularly, the present invention relates to unitary and multi-layered heat-transferable security stamps where the components of each layer within the security stamp are selected according to predefined processing goals.
Security stamps are commonly transferred from a paper or film carrier sheet to another surface under the application of heat. One common application example involves the transfer of a tax stamp to a carton or pack of cigarettes to indicate payment of applicable taxes on the product. U.S. Pat. No. 2,746,877 teaches a multi-layered dry release transfer stamp. Each of the layers utilizes specially selected solvent-based inks or coatings to enable the transfer of a visually perceptible security stamp to an associated target substrate. Other conventional transfer stamps also utilize non-aqueous solvents because they are widely available and were originally economical. However, safety concerns related to the use, storage, recovery, and disposal of non-aqueous or alcohol-based solvents have given rise to a number of OSHA regulations requiring the installation of specialized peripheral equipment for handling potentially dangerous solvents. The installation and maintenance of such peripheral equipment has driven up the cost of utilizing traditional solvents in the manufacture of transfer stamps. Further, in many instances the cost of disposing a solvent used in a particular manufacturing process has become higher than the original cost of obtaining the solvent.
There are a limited number of alternatives to the traditional solvent-based production processes. Accordingly, it is currently not possible to address the above-noted negative manufacturing issues related to the use of solvents in the production of heat transfer stamps. As a result, there continues to be a need for an economical and versatile transferable security stamp that does not necessitate the use of solvent based layers for production.
This need is met by the present invention wherein a heat-transferable security stamp and an associated manufacturing scheme are provided wherein water-borne structural components are utilized and arranged to enable more cost-effective, efficient, and safe transfer stamp production while maintaining optimal transfer stamp functionality.
In accordance with one embodiment of the present invention, a process is provided for forming a unitary heat-transferable security stamp comprising a carrier sheet, a top coat layer, at least one design layer between the carrier sheet and the top coat layer, a release layer between the carrier sheet and the design layer, and a base coat layer between the release layer and the design layer. The process comprises the steps of: (i) providing the carrier sheet; (ii) forming the release layer by presenting a water-borne adhesive release component (iii) forming the base coat layer by presenting a water-borne base coat component; (iv) forming the design layer by presenting a water-borne design component; and (v) forming the top coat layer by presenting a water-borne top coat component. The carrier sheet is selected such that it is resistant to heat above a predetermined heat transfer temperature. The adhesive release component of the release layer is selected such that it is operative to secure the carrier sheet to the base coat layer at temperatures below the heat transfer temperature and to permit release of the carrier sheet from the base coat layer at temperatures above the heat transfer temperature. The base coat component of the base coat layer is selected such that it is operative to function as a barrier between the release layer and the design layer at temperatures above and below the heat transfer temperature. The design component of the design layer is selected such that it is operative to provide an indication of the presence of the security stamp. The top coat component is selected such that it is operative to adhere to a substrate upon contact with the substrate and upon application of heat at the heat transfer temperature.
The release layer, the base coat layer, the design layer, and the top coat layer are preferably further formed by a series of drying steps, wherein respective drying steps are executed following presentation of a selected one of the layers and prior to presentation of a subsequent one of the layers. The drying step may be characterized by microwave irradiation, infrared irradiation, heated forced air drying, etc.
The carrier sheet preferably comprises a non-siliconized liner. Preferably, the release layer is applied to a major surface of the carrier sheet, the base coat layer is applied to the release layer, the design layer is applied to the base coat layer, and the top coat layer is applied to the design layer. The water-borne components may be presented as aqueous emulsions, aqueous dispersions, or aqueous solutions.
The release layer may be formed as a continuous film and may be presented as a blend of polyethylene and an aqueous paraffin wax emulsion having a melting point that is less than the heat transfer temperature.
The base coat layer may also be formed as a continuous film and may be presented as a polymeric emulsion including the base coat component. The base coat component is preferably presented so as to form a cross linked polymeric layer having a melting point that exceeds the heat transfer temperature.
The design layer is formed by presenting a polymeric emulsion including the design component and is formed in a visually perceptible pattern in the security stamp. The melting point of the design component also exceeds the heat transfer temperature. Preferably, a plurality of design layers are provided and each design layer includes a distinct design component.
The top coat layer is formed by presenting a polymeric emulsion including the top coat component and is selected such that the heat transfer temperature is at least as great as a characteristic softening temperature of the top coat.
An additional design layer may be formed in a predetermined pattern on the top coat layer. The additional design layer may be formed after formation of the remaining layers of the stamp. The additional design layer may be formed of UV fluorescent ink via an ink jet printing process and may comprise a number selected from a series of consecutive numbers.
In accordance with another embodiment of the present invention, a unitary heat-transferable security stamp is provided comprising a carrier sheet, a top coat layer, at least one design layer between the carrier sheet and the top coat layer, a release layer between the carrier sheet and the design layer, and a base coat layer between the release layer and the design layer. The security stamp is formed by a process comprising the steps of: (i) providing the carrier sheet; (ii) forming the release layer by presenting a water-borne adhesive release component; (iii) forming the base coat layer by presenting a water-borne base coat component; (iv) forming the design layer by presenting a water-borne design component; and (v) forming the top coat layer by presenting a water-borne top coat component. The carrier sheet is selected such that it is resistant to heat above a predetermined heat transfer temperature. The adhesive release component of the release layer is selected such that it is operative to secure the carrier sheet to the base coat layer at temperatures below the heat transfer temperature and to permit release of the carrier sheet from the base coat layer at temperatures above the heat transfer temperature. The base coat component of the base coat layer is selected such that it is operative to function as a barrier between the release layer and the design layer at temperatures above and below the heat transfer temperature. The design component of the design layer is selected such that it is operative to provide an indication of the presence of the security stamp. The top coat component is selected such that it is operative to adhere to a substrate upon contact with the substrate and upon application of heat at the heat transfer temperature.
In accordance with yet another embodiment of the present invention, a heat-transferable security stamp is provided comprising a carrier sheet, a top coat layer, at least one design layer between the carrier sheet and the top coat layer, a release layer between the carrier sheet and the design layer, and a base coat layer between the release layer and the design layer. The release layer includes a water-borne release component. The base coat layer includes a water-borne base coat component. The design layer includes a water-borne design component. The top coat layer includes a water-borne top coat component. The carrier sheet is resistant to heat above a predetermined heat transfer temperature. The adhesive release component of the release layer is operative to secure the carrier sheet to the base coat layer at temperatures below the heat transfer temperature and to permit release of the carrier sheet from the base coat layer at temperatures above the heat transfer temperature. The base coat component of the base coat layer is operative to function as a barrier between the release layer and the design layer at temperatures above and below the heat transfer temperature. The design component of the design layer is operative to provide an indication of the presence of the security stamp. The top coat component is operative to adhere to a substrate upon contact with the substrate and upon application of heat above the heat transfer temperature. The recited water-borne components may be capable of being dispersed in water as an aqueous emulsion, an aqueous dispersion, or as an aqueous solution.
Accordingly, it is an object of the present invention to provide an alternative transfer stamp and transfer stamp production technique that are economical, versatile, and safe. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.